Parameterizing MQTT adapter

[BobClaerhout]

I think most of the protocol adapters will almost be identical to an existing one.
For example, the actility thingpark LoraWan network sends data to the MQTT adapter on topic "accountPrefix/things/deviceEUI/uplink" and expects control commands on topic "accountPrefix/things/deviceEUI/downlink". It consists of the same functional data as the hono topics except for the path segments to be ordered differently.
I had a brief look into the code and I think changes are limited to:

• ResourceIdentifier, make IDX parameterizable:
  • private static final int IDX_ENDPOINT = 0;
  • private static final int IDX_TENANT_ID = 1;
  • private static final int IDX_RESOURCE_ID = 2;
• EndpointType:
  • parameterize the constants